Why do skeptics and debunkers passionately defend the Nazis?

I always thought the truth about the Reichstag fire was common knowledge, although I do remember scanning through a JREF post when LC:AAC was released which tried to debunk the bit about the Reichstag, but I didn't think much of it.

The Nazi plot interpretation was popularized by the classic 1960 book, The Rise and Fall of the Third Reich:

The whole truth about the Reichstag fire will probably never be known. Nearly all those who knew it are now dead, most of them slain by Hitler in the months that followed. Even at Nuremburg the mystery could not be entirely unraveled, though there is enough evidence to establish beyond a reasonable doubt that it was the Nazis who planned the arson and carried it out for their own political ends.

From Goering's Reichstag President's Palace an underground passage, built to carry the central heating system, ran to the Reichstag building. Through this tunnel Karl Ernst, a former hotel bellhop who had become the Berlin S.A. leader, led a small detachment of storm troopers on the night of February 27 to the Reichstag, where they scattered gasoline and self-igniting chemicals and then made their way quickly back to the palace the way they had come. At the same time a half-witted Dutch Communist with a passion for arson, Marinus van der Lubbe, had made his way into the huge, darkened and to him unfamiliar building and set some small fires of his own. This feeble-minded pyromaniac was a godsend to the Nazis. He had been picked up by the S.A. a few days before after having been overheard in a bar boasting that he had attempted to set fire to several buildings and that he was going to try the Reichstag next.

The coincidence that the Nazis had found a demented Communist arsonist who was out to to do exactly what they themselves had determined to do seems incredible but is nevertheless supported by the evidence. The idea for the fire almost certainly originated with Goebbels and Goering. Hans Gisevius, an official in the Prussian Ministry of the Interior at the time, testified at Nuremburg that "it was Goebbels who first thought of setting the Reichstag on fire", and Rudolf Diels, the Gestapo chief, added in an affadavit that "Goering knew exactly how the fire was to be started" and had ordered him to prepare, prior to the fire, a list of people who were to be arrested immediately after it.

Pat quoted a ScienceBlogs blog post (why are there so many truth denial blogs on that site?!) by 'Orac', which cited a couple of historical works that support the Reichstag 'lone nut' theory.

In years of meticulous research, the two authors of the book, historian Alexander Bahar and physicist and psychologist Wilfried Kugel, carried out the first comprehensive evaluation of the 50,000 pages of original court, state attorney office and secret police (Gestapo) files that had been locked away in Moscow and East Berlin until 1990. The result is a remarkable and explosive, more than 800-page document that for the first time provides almost complete circumstantial evidence that the Nazis prepared and set the Reichstag fire themselves.

[...]

Responsibility for the Reichstag Fire was a constant source of debate between German historians after the Second World War. In the early 1960’s, the attempt was made to establish the hypothesis of van der Lubbe as the sole culprit—in particular by Rudolf Augstein’s magazine Der Spiegel and the “amateur historian” and intelligence officer Fritz Tobias. To this very day, some prominent German historians base themselves on this hypothesis and still attempt to deny the guilt of the Nazis. With their new book Der Reichstagbrand, Alexander Bahar and Wilfried Kugel have provided authoritative evidence to finally dispel the longstanding controversy.

A Wikipedia user on the talk page for Marinus Van Der Lubbe calls the false-flag theory "CT nonsense" and links to a german review of Der Reichstagsbrand, which reads like one of Shermer's attack pieces - it even compares people who believe the fire was a Nazi plot to Holocaust deniers!